“Article 1 Section 8. Powers enumerated to Congress by the Constitution.”
And where does that say the power to govern naturalization does not include the power to define citizenship?
It does not.
The power to naturalize includes the power to define citizenship. There is no distinction.
In fact, Section 5 of the 14th Amendment explicitly gives Congress the power to define and implement citizenship. (The power to implement includes the power to clear up confusion, uncertainty, or lacking definitions.)
The necessary and proper clause extends Article 1 Section 8. Powers enumerated to Congress by the Constitution to allow Congress to define citizenship.
Actually there is a difference. Congress cannot define citizenship. If Congress could define citizenship, they could enact a law that prevents a particular person or persons from being a citizen or NBC. They could decide who they want are NBCs and who aren’t. They could say only the political elites are NBCs and everyone else is not as they could enact a law and it would be constitutional according to your BS theory.